1. Field of the Invention
The present invention relates in general to artificial substances having a structure of diamond crystal and methods for producing the same, and more particularly to a method of artificially producing substances (which will be referred to as "c-BCN" hereinafter), which have a structure of diamond crystal, by applying dynamic high pressure to graphite or graphite-like subsance (which will be referred to as "h-BCN" hereinafter) which is composed of boron (B), carbon (C) and nitrogen (N) as main elements.
2. Description of Prior Art
As is known, both diamond and boron nitride of tesseral system (which will be referred to as c-BN hereinafter) having a crystal structure similar to that of the diamond are extremely hard and thus commonly applied to the manufacture of abrasive materials and cutting tools which are indispensable to the industrial field. Besides, in recent years, some of these substances have been used as the material for semiconductors. Although the diamond is the hardest substance, it is oxidized in oxidative atmosphere of high temperature as is known from the fact that it burns in air. Furthermore, the diamond has a tendency to be eroded when it is in contact with by any of materials of the group VIII elements or with alloys containing the metal such as iron, nickel or cobalt. Although the Vickers hardness is about a half of that of diamond, the c-BN does not have the above-mentioned drawbacks possessed by the diamond. Thus, in recent years, the c-BN has been taken notice of the material particularly applicable for the abrasive materials and cutting tools for ironwork.
Accordingly, if c-BCN substance of tesseral system (viz., a substance in which a part of crystal lattice in diamond is substituted with some boron (B) and nitrogen (N)) can be produced, the substance is expected to possess both the mechanical strength of the diamond and the chemical stability of the c-BN. That is, the substance is expected to be epock-making highly strong material.
Hitherto, for synthesizing the c-BCN substances of such tesseral system, various methods have been proposed and put into practical use. One is a method in which a h-BCN substance of hexagonal system is treated statically at temperature of 3600.degree. C. and pressure of 14 GPa (A. R. Badzian, Mater, Res, Bull., 16 (1981) 1385)). One is a method in which a h-BCN powder of hexagonal or amorphous system is mixed with a bit of metal of iron family elements and sintered under superhigh pressure and temperature (Japanese Patent First Provisional Publication 55-67570). In this method, an installation disclosed in Japanese 38-14 was used. One is a method in which a h-BCN substance containing only 0.02 to 2.0% carbon is treated at temperature of 1300.degree. to 1600.degree. C. and pressure of 4 to 6 GPa (Japanse Patent First Provisional Publication 58-120505). One is a method in which a h-BCN substance of hexagonal or amorphous system is treated with a solvent at temperature higher than 1300.degree. C. and pressure higher than 5 GPa (Japanese Patent First Provisional Publication 61-24328). In this method, a device disclosed in U.S. Pat. No. 2,941,248 was used. One is a method in which a h-BCN substance of hexagonal system is statically treated at pressure of 14 GPa and temperature of 3300.degree. C. and one is a method in which a h-BCN substance of hexagonal system is treated statically at pressure of 7.5 GPa and high temperature using, as catalyst, a metal of iron or aluminium family elements (Takayoshi SASAKI, Yoshinori FUJIKI, "Gypsum & Lime" No. 219, P45-50, 1989).
In addition to the above-mentioned methods, various attempts have been also carried out for production of the c-BCN substances by using a solvent under a condition of high pressure and high temperature.
One attempt (T. Sasaki et al., Chem. Mater. 5 ,1993, 695) revealed however that a c-BCN substance produced by statically treating a h-BCN substance together with a cobalt solvent at pressure of 5.5 GPa and temperature of 1400.degree. to 1600.degree. C. was just a mixture of diamond and c-BN susbstance. That is, it has been revealed that a desired c-BCN substance of tesseral system can not be produced under the static high pressure. This is because an essential problem which should be solved when synthesizing substances which are not present in the natural world is not solved by such static high pressure and high temperature treatment. It is considered that, under equilibrium condition of such process, separation of diamond and c-BN is natural in thermodynamic point of view.